This invention relates to the field of gas turbines and more specifically to components in gas turbines that are exposed to hot gases.
The degree of efficiency of gas turbines depends to a special degree on an efficient use of cooling air. Both operational safety and the assurance of a justifiable life span of the components heated during operation make adequate cooling indispensable. Accordingly, there has always been a concentration on optimizing the cooling of gas turbines.
Components that are surrounded by a flow of hot gases during the operation of the gas turbine, and thus must be cooled appropriately, can be cooled in several ways. On the one hand, it is possible to provide a so-called film cooling, in which cooling air is in a targeted manner passed around the outside surface of the component. On the other hand, a so-called internal cooling can be achieved, whereby the component has cooling channels inside, through which a flow takes place. The internal cooling presupposes that the components are hollow profiles or are at least provided with channels, and that the latter permit good heat transfer from the outside material parts to the cooling air. These two cooling methods are frequently used in combination, since, on the one hand, the internal cooling is only possible in areas where the thickness of the material of the component permits construction as a hollow profile or the attachment of drilled channel openings, and since, on the other hand, an effective film cooling requires good distribution of the cooling air on the outside surfaces. Effective film cooling is only possible in the case of larger surfaces, a strong flow, and, if possible, a low cooling air volume, if the cooling air is supplied at least in part via internal cooling channels.
When constructing such components as hollow profiles, a problem that occurs frequently is that the channels have areas in which the cooling air is deflected, resulting in so-called flow stagnation areas in which the flow becomes distinctly three-dimensional, and in which the cooling then becomes less efficient (so-called xe2x80x9cdead water areasxe2x80x9d). Such flow stagnation areas in most cases result necessarily from the geometric parameters of the components and channels on the one hand, and, on the other hand, from the fact that a design of the cooling channels that would guide the flow in an optimal way, especially in the deflection areas, would require rounded areas in the corners. But such massive rounded areas, i.e. constructed by filling them with material, would however cause the corners to become heavier, which means that moving components, such as turbine blades, would become less economical and deflection areas and bends in such corners would be cooled even less well. The formation of such flow stagnation areas is often counteracted by integrating ribs or guide plates that specifically supply and remove the cooling air to/from such areas, but such means are often not sufficient to make cooling in the deflection areas efficient enough.
The invention therefore is based on the objective of providing a component for gas turbines that has internal cooling, in which during operation of the gas turbine, i.e. while hot air flows around the component, and while cooling air simultaneously flows through the component, efficient cooling is made possible in the deflection areas of the cooling air.
This objective is achieved by an arrangement of drilled openings in the flow stagnation zones on the outflow sides of the deflection areas so that these zones are no longer actual dead water areas. The drilled openings provided there cause a flow through the zones and thus have the result that the cooling air is not retained too long in these zones. The cooling efficiency in these areas improves according to the reduced staying time of the cooling air in the flow stagnation zones. The cooling air flowing out of the drilled opening or openings onto the outside, then can simultaneously still be utilized for film cooling on the outside of the component if the drilled opening has been located at a suitable place. The drilled opening or openings can preferably be located on the pressure side in the outside wall facing the flowing air. The exiting cooling air in this way flows around the outside surface to the suction side of the component and acts not only as a ventilation of the flow stagnation zones but also as a film cooling along the path around the component on the suction side.
A preferred embodiment of the invention includes a turbine blade around which a hot working air stream flows. The guide walls in the turbine blade are arranged essentially radially of the rotation axis of the turbine rotor and essentially vertically to the plane of the turbine blade outside surface between the outside walls. The radially extending cooling channels formed in this way are connected in pairs at the tip of the turbine blade in a flow connection; and that in this connection a deflection area of the cooling channels is arranged in the area of the tip. Especially in components designed in this way, the problem of cooling is manifested particularly in the deflection areas. The tips of the turbine blades are exposed to a high mechanical and thermal load during operation, and without sufficient cooling a severe fatigue and wear of the materials in the tip area can hardly be prevented. On the other hand, the geometry of the tips is more or less determined by the function of the blades, and the design of the channels therefore must adapt to it. Especially in the deflection area of the cooling channels that are supplied with cooling air from the hub area, and through which the cooling air flows in a U-shape, significant stagnation zones form; but their cooling efficiency-reducing effect can be prevented or at least greatly reduced by drilled openings.
The arrangement of the drilled openings in the flow stagnation zone on the outflow side is found to be particularly advantageous in combination with, for example, drilled openings arranged on the inflow side and extending essentially radially to the rotation axis of the turbine motor through a tip cover that closes off the hollow profile of the component radially.
These radial drilled openings can also be arranged in an approximate L-shape, i.e. both next to each other, parallel to the tip cover, as well as next to each other, radially along the rear guide wall, around the corner on the outflow side. A group of drilled openings arranged in a two-dimensional, for example triangular, shape that covers an area of the stagnation zone and, for example, in a way connects the two legs of the L""s with each other, can also be advantageous.